Can anyone let me know their successful jetting spec for a 1976 250 MC5.
I'm having really bad over fuelling problems in the mid range. I'm going to be experimenting with a new needle jet at 2.74 down from 2.85 and a brand new needle. Just curious to know what other owners have settled on. The bike is not run at altitude. Thanks in advance.
That is a big drop in needle jet and pretty lean for a 250. If your old needle jet has been in the carb awhile it is probably ovalized and running rich because of that. Most of the time when I see a Bing blubbering or loading in the middle it is because of two things. A worn needle jet and a worn slide. If the slide has worn a smiley face into it then you should also replace it. Most 250 Pentons I have had ran a 280 or 283 Needle jet.
Larry P
I have a 77 250. My notes show 180 main, 2H1 needle and a 316 needle jet. That's for sea level and I've been as high as 4 to 5 thousand feet without any issues. Call Charlie at Bing, he can tell you the stock settings. He will want the carb number.
Mike
Before you start chasing jet size to make it run right, remember it ran right once with what it has in it. So something changed.
Larry P
I agree. Those were the stock sizes that were in the bike, with that carb number, when it was new, according to Bing.
Mike
Thanks All. I didn't know the stock needle jet size for my baseline so I'll follow advice and try a new 285. I have to say the one I removed looks OK and not ovaled, but almost impossible to detect I guess using 56 year old eyes!. Slide looks OK. I'll let you know how I get on.